Etching and mechanical grinding film-layers stacked on a semiconductor substrate

ABSTRACT

In some embodiments, a method includes wet-etching a first film layer of a plurality of film layers stacked on a semiconductor substrate, the wet-etching of the first film layer performed using a first chemical, where the first film layer is an outermost film layer stacked on the semiconductor substrate. The method further includes wet-etching a second film layer of the plurality of film layers using a second chemical. The method also includes using a mechanical grinding wheel to grind the semiconductor substrate to reduce a thickness of the semiconductor substrate.

BACKGROUND

Technological advancements have enabled the semiconductor industry tosuccessfully scale down the sizes of transistors on integrated circuits,resulting in substantial reductions in integrated circuit (“IC”) sizes.In addition, improved manufacturing processes have allowed circuitdesigners and process engineers to increase the number of transistors onICs by increasing the sizes of the wafers.

SUMMARY

According to an embodiment, a method includes wet-etching a first filmlayer of a plurality of film layers stacked on a semiconductorsubstrate, the wet-etching of the first film layer performed using afirst chemical, and the first film layer is an outermost film layerstacked on the semiconductor substrate. The method also includeswet-etching a second film layer of the plurality of film layers using asecond chemical. Further the method includes using a mechanical grindingwheel to grind the semiconductor substrate to reduce a thickness of thesemiconductor substrate.

According to another embodiment, a method of thinning of a semiconductorwafer includes protecting a front side of a semiconductor substrateusing tape. The method further includes chemically etching a pluralityof film layers stacked on the semiconductor substrate to expose thesemiconductor substrate, the chemical etching performed using a firstchemical selected to etch a first film layer and a second chemicalselected to etch a second film layer. The method further includesgrinding the semiconductor substrate to reduce a thickness of thesemiconductor substrate.

According to yet another embodiment, a method includes providing asemiconductor substrate having an integrated circuit formed on a firstside of the semiconductor substrate and having a silicon nitride filmlayer and a polysilicon film layer stacked on a second side of thesubstrate. The method further includes removing the silicon nitride filmlayer using a first chemical bath comprising 30-49% hydrogen fluoride,inclusive. The method further includes removing the polysilicon filmlayer using a second chemical bath comprising 60-70% nitric acid,inclusive and 0.5%-1% hydrogen fluoride, inclusive, to expose thesemiconductor substrate. The method also includes thinning thesemiconductor substrate using a mechanical grinder.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various examples, reference will now bemade to the accompanying drawings in which:

FIG. 1(a) is a perspective view of a semiconductor wafer used tomanufacture integrated circuits, in accordance with various examples.

FIG. 1(b) is an inverted side view of a portion of the semiconductorwafer of FIG. 1(a), in accordance with various examples.

FIG. 1(c)-1(f) are inverted side views of the portion of thesemiconductor wafer depicted in FIG. 1(b) and depict the removal of aseries of film layers, in accordance with various examples.

FIG. 1(g) is an inverted side view of the portion of the semiconductorwafer depicted in FIG. 1(b) and depicts the grinding of a semiconductorsubstrate, in accordance with various examples.

FIG. 2 is an illustrative flowchart of a method for thinning asemiconductor wafer, in accordance with various embodiments.

FIG. 3 is another illustrative flowchart of a method for thinning asemiconductor wafer, in accordance with various embodiments.

FIG. 4 is yet another illustrative flowchart of a method for thinning asemiconductor wafer, in accordance with various embodiments.

DETAILED DESCRIPTION

The size of an IC chip is usually not a concern when the chip is placedin an automobile, desktop computer, or other relatively large device.However, the size of the chip is of greater importance when the chip isplaced in a miniature device, such as a smartphone. A reduction in theoverall size of the IC package may be achieved using high-densitypackaging. High-density packaging is typically done by stacking multipleintegrated circuits. Package density may be further improved by reducingthe thickness of the wafer—used to fabricate a few thousand ICs atonce—by performing wafer backgrinding (also commonly referred to as“wafer thinning”). Wafer backgrinding involves thinning semiconductorwafers after ICs have been fabricated onto the wafer.

Mechanical wheel grinders are employed to remove unnecessary siliconsubstrate from the backside of the semiconductor wafer. In some cases,the backside of the semiconductor wafer includes an extraneous stack offilm layers, which leads to an increase in the overall thickness of thehigh-density package. In such cases, a reduction in the thickness of thewafer is achieved by removing both the extraneous film layers and aportion of the silicon substrate from the backside of the wafer bymechanical wheel grinders. In some cases, the film layers on thebackside of the semiconductor wafer are grind-resistant and/or hard suchthat the mechanical wheel grinders are damaged during the grindingprocess. Replacement of a damaged mechanical wheel grinder is expensiveand performing semiconductor wafer thinning using a damaged wheel canfurther damage the semiconductor wafer. Thus, there is a need in the artfor methods to prevent damage to the mechanical wheel grinders.

The present disclosure provides techniques to prevent damage tomechanical wheel grinders during the removal of film layers stacked onthe backsides of semiconductor wafers. More specifically, the presentdisclosure relates to replacing the mechanical wheel grinding techniqueemployed to remove the film layers present on the backsides of thewafers with a wet-etching technique. In some embodiments, backside waferthinning is performed by first wet-etching the film layers and thenwheel-grinding the semiconductor substrate to thin the substrate. Inthis way, the mechanical wheel grinder is not used to remove filmlayers—some of which have hardness characteristics equivalent to thoseof a diamond—from the backside of the semiconductor wafer, and so theintegrity of the mechanical wheel grinder is preserved.

FIG. 1(a) is a perspective view of an illustrative semiconductor wafer100 used to manufacture integrated circuits. The wafer 100 may compriseany suitable compound (e.g., silicon, gallium arsenide and indiumphosphide). Although the following discussion assumes wafers made ofsilicon, the techniques described herein may apply to wafers made fromother compounds (e.g., elements from column IV of the periodic table ofelements as well as combinations of elements from columns III-V).

Fabrication processes are performed on a front side 110 of thesemiconductor wafer 100 to produce a plurality of integrated circuits(not expressly depicted in FIG. 1(a)). For example, an average-sized(e.g., 300 mm) semiconductor wafer can produce thousands of ICs. Asnoted above, as technology leads electronics to shrink in size, ICpackaged devices must be reduced both in footprint and thickness.Reduction in packaged device size is often achieved by reducing the ICthickness. For high yield, the reduction of IC thickness is oftencombined with an increased wafer diameter. However, a largersemiconductor diameter may sometimes require a “thicker” semiconductorwafer that can withstand the semiconductor fabrication and wafermanufacturing processes. For the semiconductor wafer 100, numeral 105,as further discussed below, depicts the wafer thickness. FIG. 1(a) alsoshows the backside 115 of the semiconductor wafer 100. Hard film layersare formed on and subsequently wet-etched from the backside 115, asdescribed below.

FIG. 1(b) is an inverted side view of a portion 120 of the semiconductorwafer 100 in accordance with some embodiments. The portion 120 is anillustrative portion of the semiconductor wafer 100 and is used todescribe the fabrication process that can be performed on the wafer 100.The methods described in this disclosure can also be employed on thecomplete semiconductor wafer 100.

The inverted side view of the portion 120 of the wafer 100 includes asemiconductor substrate 200. The front side 110 refers to a surface ofthe substrate 200 opposite the film layers 205, 210, 215 and 220. Thebackside 115 refers to the surface of the outermost film layer 205, 210,215, 220 opposite the substrate 200. More specifically, in FIG. 1(b),the backside 115 refers to the surface of the film layer 220 oppositethe substrate 200, but during film layer removal, the film layer havingthe backside 115 may change. For example, when the film layer 220 isremoved, the backside 115 refers to the surface of the film layer 215opposite the substrate 200. Similarly, when film layer 215 is removed,the backside 115 then refers to the surface of the film layer 210opposite the substrate 200. When the film layer 210 is removed, thebackside 115 refers to the surface of the film layer 205 opposite thesubstrate 200. When the film layer 205 is removed, the backside 115refers to the surface of the semiconductor substrate 200 opposite thefront side 110.

FIG. 1(b) also depicts a thickness 105 of the portion 120. The filmlayers 205, 210, 215, 220, as further described below, can be extraneousor can be intentionally deposited on the substrate 200. The film layers205, 210, 215, 220 are termed “extraneous” or “process-films,” when theyaccumulate and form a layer on the backside of the semiconductorsubstrate 200 due to the fabrication processes performed on the frontside 110. For example—silicon oxide or silicon nitride used in the frontside 110 to fabricate the ICs may form process-films on the backside115. And the film layers 205, 210, 215, 220 can be intentionallydeposited to prevent doping contamination. When intentionally deposited,these layers are referred to as “back-seal” films.

The film layers 205, 210, 215 and 220 may also be intentionally formedon the substrate 200 using fabrication processing techniques. Inparticular, semiconductor wafer fabrication processing can include manyprocess steps, such as surface cleaning, epitaxy, oxidation,diffusion/implantation, photolithography, etching, layer deposition,multiprobe, and backgrinding. These steps often involve reactivechemicals such as hydrofluoric acid, which is particularly useful inetching oxides and nitrides. Furthermore, various manufacturers supplythe equipment used in wafer production, and there is no standard on howthe equipment interfaces with the wafer. As such, a large variety ofhandling systems are used that have little in common with each otherexcept that they all handle the wafer. Thus, it is important that thewafer be designed to withstand the fabrication process in order tosupport high yield and profitability. The problem noted above is inlarge part addressed by coating the wafer with a thin film or coating.Thus, in some embodiments, the film layers 205, 210, 215, 220 arenecessary and intentionally grown on the backside of the wafer as theyprovide mechanical strength to the wafer for the processes to beperformed on the front side 110 to fabricate the IC. For example, thebackside of the semiconductor wafer 100 can be covered with siliconnitride, silicon dioxide, polysilicon etc. In some embodiments, the filmlayers 205, 210, 215, 220 prevent dopants from diffusing out of thesubstrate 200. The methods of producing silicon nitride includenitriding and low pressure chemical vapor deposition (LPCVD). Other CVDtechniques can be used to generate film layers on the backside of thesemiconductor wafer.

Referring again to FIG. 1(b), the film layers 205, 210, 215, 220 can beremoved layer-by-layer using a wet-etching process. FIG. 1(c) depictsthe portion 120 with the outermost film layer 220 removed by wetetching. Similarly, FIG. 1(d), FIG. 1(e), and FIG. 1(f) depict theportion 120 with the film layers 215, 210, and 205 removed,respectively. In some embodiments, film layers 205, 210, 215, and 220can include silicon nitride, silicon dioxide, polysilicon, etc. and arewet-etched using chemical baths specific to the outermost film layer(i.e., chemical baths containing chemicals which can selectively etchesthe outermost layer on the backside 115). Typically, an oxide layer or asilicon nitride layer is wet-etched using a chemical bath including30-49%, inclusive, of hydrogen fluoride. A polysilicon layer can bewet-etched using a chemical bath including 60-70%, inclusive, of nitricacid and 0.5-1%, inclusive, of hydrogen fluoride. FIG. 1(g) depicts thebackside 115 of the substrate 200 having been subjected to a mechanicalwheel grinding process to remove a portion of the substrate 200 from thebackside 115. The amount of the substrate 200 that is removed isapplication-specific and may be determined as is suitable.

FIG. 2 depicts a method 300 for thinning a semiconductor wafer, such asthe portion 120 depicted in FIG. 1(b). The method 300 disclosed in FIG.2 is now described in tandem with FIG. 1(b). The method 300 generallyincludes wet-etching all the film layers 205, 210, 215, 220 from thebackside 115 and then mechanically grinding the semiconductor substrate200 from the backside 115. Wet-etching can be done using variousdifferent processes as would be familiar to one of ordinary skill in theart. Common examples include bath etch, spin etch, etc. As such,although the following discussion assumes wet-etching done using achemical bath, the following principles may equally apply to wet-etchingdone using different techniques (e.g., spin etch, splash etch, bubbleetch, chemical etch, etc.).

In some embodiments, the number of film layers on the semiconductorsubstrate 200 can vary and may not be present in the same number asdepicted in FIG. 1(b), as the number of film layers depends on thefabrication processes to be performed on the front side 110 of thesemiconductor substrate 200. In some embodiments, there are more filmlayers than shown in FIG. 1(b). In other embodiments, the number of filmlayers is fewer than the number of film layers shown in FIG. 1(b). Themethod 300 may be modified as necessary to wet-etch some or all filmlayers formed on a particular semiconductor substrate 200.

The method 300 begins in step 310 with wet-etching a first film layer ofthe plurality of film layers 205, 210, 215, 220 stacked on the backsideof the semiconductor substrate 200 using a first chemical. The firstlayer to be wet-etched will be the outermost layer, and in thisembodiment the outermost layer is marked 220. Consider, as an example,that the film layer 220 is a silicon nitride layer. The silicon nitridelayer can be wet-etched using a chemical bath including 30-49%,inclusive, of hydrogen fluoride. In other embodiments, the film layer220 is an oxide layer which can also be wet-etched using a chemical bathincluding 30-49% hydrogen fluoride, inclusive. In another embodiment,the film layer 220 may be a polysilicon layer which can be wet-etchedusing a chemical bath including 60-70% nitric acid, inclusive and 0.5-1%hydrogen fluoride, inclusive. Wet-etching of the film layer 220 maycontinue until the bath containing the chemical which selectively etchesthe film layer 220 completely.

The method 300 continues in step 320 with wet-etching a second filmlayer. With respect to FIG. 1(b), the film layer 215 is the secondlayer. The second layer can be an oxide layer, a silicon nitride layer,a poly-silicon layer, etc. Wet-etching an oxide layer and a siliconnitride layer can utilize a chemical bath including 30-49%, inclusive,of hydrogen fluoride. A polysilicon layer can be wet-etched using achemical bath including 60-70% nitric acid, inclusive and 0.5-1%hydrogen fluoride, inclusive. As noted above, the number of film layerscan vary. In some embodiments, there are more than two film layers onthe backside of the semiconductor wafer, as depicted in FIG. 1(b). Asimilar wet-etching process can be used to remove such additional filmlayers. In some embodiments, depending on the chemical composition ofthe film layer, a chemical bath including 30-49% hydrogen fluoride,inclusive or 60-70% nitric acid, inclusive and 0.5-1% hydrogen fluoride,inclusive can be used to selectively wet-etch the layers 210 and 205.

As mentioned above, a reduction in the thickness of the wafer 100 isachieved by removing the film layers by wet-etching and by removing aportion of the silicon substrate 200 by mechanical wheel grinding. Step310 and 320 remove extraneous film layers (e.g., film layers 205, 210,215 and 220) from the semiconductor substrate 200. Once the siliconsubstrate is exposed, the method of claim 300 further continues in step330 with backgrinding the semiconductor substrate 200 (FIG. 1(b)).Backgrinding is performed to remove a portion of the semiconductorsubstrate 200. In some embodiments, to improve the productivity of thegrinding operation, a multi-step grinding operation is performed. Thefirst step of the multi-step grinding operation comprises using a largegrit to coarsely grind the semiconductor substrate 200 to remove thebulk of the excess substrate thickness. The degree to which thesubstrate thickness is reduced is variable and application-dependent.The second step of the multi-step grinding operation comprises using afiner grit to polish the wafer and to accurately grind the substrate tothe desired thickness, which, as mentioned, is application-specific. Thegrinding operation begins on the surface of the substrate 200 previouslyabutting the film layer 205 (i.e., on the backside 115) and progressestoward the opposing surface of the substrate 200 at the front side 110.In some embodiments, the chemical bath including 60-70% nitric acid,inclusive, and 0.5-1% hydrogen fluoride, inclusive, can be utilized toremove a portion of the substrate 200.

FIG. 3 depicts a modified wafer thinning method 400. Referring to FIGS.1(b) and 3, the modified wafer thinning technique includes taping thefront side 110, chemically removing the film layers 205, 210, 215, and220, and mechanically removing (i.e., grinding) a portion of thesemiconductor substrate 200. Wet-etching can be done using variousdifferent processes, such as bath etch, spin etch, etc. As such,although the present discussion assumes wet-etching performed using achemical bath, the principles disclosed herein may apply to wet-etchingdone using different techniques (e.g., spin etch, splash etch, bubbleetch, chemical etch, etc.).

The method 400 begins in step 410 with protecting the front side 110 ofthe semiconductor wafer 100 using tape. Any suitable type of tape, suchas UV (ultraviolet)-curable backgrinding tape, or a non-UV tape, may beused to ensure protection against wafer surface damage duringbackgrinding and to prevent wafer surface contamination caused byinfiltration of grinding fluid and/or debris. The method 400 continuesin step 420 with chemically etching a plurality of film layers stackedon the substrate 200. As noted above, the number of film layers presenton the substrate 200 may depend on the mechanical strength needed by thesemiconductor wafer 100 for the processes to be performed on the frontside 110 to fabricate the ICs. As noted above, in some cases, the filmlayers may also be present to avoid doping contamination (“back-seal”films). Additionally, in some cases, the number of film layers presenton the substrate 200 depends on the fabrication processes performed onthe frontside 110.

The chemical etching of step 420 is selective in nature. In particular,the film layers are selectively etched using chemicals capable ofetching each of the film layers 205, 210, 215, and 220. For example, afilm layer can be a silicon nitride layer, a silicon oxide layer, apolysilicon layer, etc. Certain chemicals selectively etch—one layer ata time—each of the above-mentioned film layers. For instance, a chemicalbath including 30-49% hydrogen fluoride, inclusive, can be used toremove a silicon nitride layer and a silicon oxide layer and a chemicalbath including 60-70% nitric acid, inclusive, and 0.5-1% hydrogenfluoride, inclusive, can remove a polysilicon layer. The chemical bathremoves the topmost layer and the removal process essentially stops whenthe topmost layer is removed as the chemical bath used is a selectiveetchant. Thus, for example, if the topmost layer is silicon nitride, thechemical bath including 30-49% hydrogen fluoride will be utilized, butthis chemical bath will cease etching once the silicon nitride layer isremoved. Assume, as an example, that after removing the silicon nitridelayer, the polysilicon layer becomes the topmost layer. A differentchemical bath including 60-70% nitric acid, inclusive, and 0.5-1%hydrogen fluoride, inclusive, can be used to etch the polysilicon layer.In this manner, the step 420 chemically removes the plurality ofbackside film layers until the semiconductor substrate 200 is exposed.In some embodiments, the chemical bath including 60-70% nitric acid,inclusive, and 0.5-1% hydrogen fluoride, inclusive, can be utilized toremove a portion of the substrate 200.

The method 400 further continues in block 430 with backgrinding thesemiconductor substrate 200. As noted above, a reduction in thethickness of the semiconductor wafer 100 is achieved by removing thefilm layers 205, 210, 215, and 220 by wet-etching and by removing aportion of the substrate 200 by mechanical wheel grinding. Backgrindingis performed using a mechanical grinder and in this embodiment, thebackgrinder removes a portion of the semiconductor substrate 200. Insome embodiments, to improve the productivity of the grinding operation,a multi-step grinding operation is generally performed. The first stepuses a large grit to coarsely grind the wafer and to remove a bulk ofthe excess substrate thickness. A finer grit is then used in the secondstep to polish the substrate and to accurately grind the substrate tothe desired thickness.

FIG. 4 depicts an illustrative method 500 to wet-etch the backside filmlayers 205, 210, 215, and 200 and to mechanically grind the substrate200, and this method 500 is now described in tandem with FIG. 1(b). Step510 includes providing a semiconductor substrate 200 having ICs formedon the front side 110 and having backside film layers that can include asilicon nitride film layer and a polysilicon film layer. The positionsof layers are interchangeable; that is, either of the film layers can bethe outermost layer. The method 500 continues in step 520 with removingthe silicon nitride film layer using a chemical which can selectivelyetch the silicon nitride film. For example, a chemical bath including30-49% hydrogen fluoride, inclusive, can be utilized to remove thesilicon nitride layer. After etching the silicon nitride layer, thewet-etching of the exposed layer (e.g., polysilicon film layer) isineffective with the chemical bath used to etch nitride film. Thus,wet-etching, for practical purposes, is said to have stopped afteretching the specific layer that the chemical bath is selected to etch.

The method 500 continues in step 530 with removing the exposed layer,i.e., the polysilicon layer, using a different chemical bath including60-70% nitric acid, inclusive, and 0.5-1% hydrogen fluoride, inclusive.The method of claim 500 continues in step 540 with backgrinding theexposed semiconductor substrate 200. Backgrinding is performed using amechanical grinder to remove a portion of the semiconductor substrate200. In some embodiments, to improve the productivity of the grindingoperation, a multi-step grinding operation is generally performed. Thefirst step uses a large grit to coarsely grind the substrate and toremove a bulk of the excess substrate thickness. A finer grit is used inthe second step to polish the substrate and to accurately grind thesubstrate to the desired thickness. In some embodiments, the chemicalbath including 60-70% nitric acid, inclusive, and 0.5-1% hydrogenfluoride, can be utilized to remove a portion of the substrate 200.

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present disclosure. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the followingclaims be interpreted to embrace all such variations and modifications.

What is claimed is:
 1. A method, comprising: wet-etching a first filmlayer of a plurality of film layers stacked on a first side of asemiconductor substrate, the wet-etching of the first film layerperformed using a first chemical, wherein the first film layer is anoutermost film layer stacked on the semiconductor substrate; wet-etchinga second film layer of the plurality of film layers using a secondchemical; and using a mechanical grinding wheel to grind thesemiconductor substrate from the first side to reduce a thickness of thesemiconductor substrate.
 2. The method of claim 1, further comprisingcommencing the grinding of the semiconductor substrate on a surface ofthe substrate previously abutting at least one of the plurality of filmlayers.
 3. The method of claim 1, wherein the first film layer comprisesa silicon nitride layer, and wherein the first chemical comprises30%-49% hydrogen fluoride, inclusive.
 4. The method of claim 1, whereinthe second film layer comprises a poly-silicon layer, and wherein thesecond chemical comprises 60%-70% nitric acid, inclusive and 0.5%-1%hydrogen fluoride, inclusive.
 5. The method of claim 1, wherein thefirst film layer comprises a poly-silicon layer, and wherein the firstchemical comprises 60%-70% nitric acid, inclusive and 0.5%-1% hydrogenfluoride, inclusive.
 6. The method of claim 1, wherein the second filmlayer comprises a silicon nitride layer, and wherein the second chemicalcomprises 30%-49% hydrogen fluoride, inclusive.
 7. The method of claim1, wherein the first film layer comprises a silicon oxide layer, andwherein the first chemical comprises 30%-49% hydrogen fluoride,inclusive.
 8. The method of claim 1, wherein the second film layercomprises a silicon oxide layer, and wherein the second chemicalcomprises 30%-49% hydrogen fluoride, inclusive.
 9. The method of claim1, wherein the plurality of film layers stacked on the semiconductorsubstrate are derived from a plurality of microfabrication processesperformed on a front side of the semiconductor substrate.
 10. A methodof thinning a semiconductor wafer, comprising: protecting a front sideof a semiconductor substrate using tape; chemically etching a pluralityof film layers stacked on a backside of the semiconductor substrate toexpose the backside of the semiconductor substrate, the chemical etchingperformed using a first chemical that etches a first film layer and asecond chemical that etches a second film layer; and grinding thebackside of the semiconductor substrate to reduce a thickness of thesemiconductor substrate.
 11. The method of claim 10, wherein the firstchemical comprises 30%-49% hydrogen fluoride, inclusive, and wherein thefirst film layer comprises silicon nitride.
 12. The method of claim 10,wherein the second chemical comprises 60%-70% nitric acid, inclusive and0.5%-1% hydrogen fluoride, inclusive, and wherein the second film layercomprises polysilicon.
 13. The method of claim 10, wherein the firstchemical comprises 30%-49% hydrogen fluoride, inclusive, and wherein thefirst film layer comprises silicon dioxide.
 14. The method of claim 10,wherein the tape comprises an ultraviolet curable back-grinding tape.15. The method of claim 10, wherein the plurality of film layers stackedon the semiconductor substrate are formed from a plurality of sequentialmicrofabrication processes performed on the front side of thesemiconductor substrate.
 16. A method, comprising: providing asemiconductor substrate having an integrated circuit formed on a firstside of the semiconductor substrate and having a silicon nitride filmlayer and a polysilicon film layer stacked on a second side of thesubstrate; removing the silicon nitride film layer using a firstchemical bath comprising 30-49% hydrogen fluoride, inclusive; removingthe polysilicon film layer using a second chemical bath comprising60-70% nitric acid, inclusive and 0.5%-1% hydrogen fluoride, inclusiveto expose the semiconductor substrate; and thinning the semiconductorsubstrate from the second side using a mechanical grinder.
 17. Themethod of claim 16, further comprising performing a plurality ofmicrofabrication processes on the first side of the semiconductorsubstrate to produce the integrated circuit, wherein themicrofabrication processes form the silicon nitride film layer and thepolysilicon film layer stacked on the second side of the semiconductorsubstrate.
 18. The method of claim 16 further comprising removing asilicon oxide layer using the first chemical bath.
 19. The method ofclaim 16 further comprising protecting a front side of a semiconductorsubstrate using tape.
 20. The method of claim 16 further comprisingremoving a portion of the semiconductor substrate using the secondchemical bath.